Question

According to an on-line dating website, 20% of the couples who are in committed relationships met on-line. Suppose you know 15 couples in a committed relationship. What is the expected number of couples who met on-line? What is the standard deviation?

Answer 1

15/x = 20/100
15*100 = 20*x
1500 = 20x
1500/20 = 20x/20
75 = x

15/75 = 20/100

the expected number of couples who met online is 75